Method of manufacturing submarine cables



y 1963 E. COOKE ETAL 3,09

METHOD OF MANUFACTURING SUBMARINE CABLES Filed Feb. 23, 1960 C TAPE PREGNATED WITH C0RR0S|ON INHIBITOR, E. 6., BARIUM CHROMATE B-POLYTHENE SHEATH' ALUMINIUM TAPES-6 POLYTHENE INSULATION-5 COPPER TAPE FORMED INTO A TUBE OVER THE HEART AND THEN MECH ANICALLY REDUCED IN DIAMETER.

IN VEA/TORS.

Eflu ARfi ZINE/{AM chrrk' FAM AxTHu/a Don ELAN United States Patent METHOD OF MANUFACTURING SUBMARINE CABLES Edward Ingram Cooke, London, and James Arthur Donelan, Harrow, England, assignors to Submarine Cables Limited and Pirelli General Cable Works Limited, both of London, England Filed Feb. 23, 1960, Ser. No. 10,311 Claims priority, application Great Britain Feb. 27, 1959 5 Claims. (Cl. 29-460) This invention relates to submarine cables and is more particularly concerned with submarine coaxial cables having insulation extruded over an inner conductor which surrounds a stranded metal heater. Submarine cables of this nature are described in British patent specifications Nos. 703,782 and 740,647 and in an article entitled A New Deep-Sea Coaxial Cable contained in the Journal of The Institution of Electrical Engineers, volume 2 (new series), pages 572 to 573, October 1956. The above mentioned references described an armourless submarine coaxial cable having an inner conductor which surrounds a stranded heart of high tensile steel but the invention may also be used for the armoured shore end portions of such cables in which the stranded heart is of steel wires to simulate the electrical characteristics of the deep-sea portion of the cable.

It has already been proposed to use, as an inner conductor for the above mentioned cables, a copper tape longitudinally folded about the stranded metal heart with the longitudinal edges of the tape either abutting, or locked in a box-seam. Further, experiments have been carried outwith the edges overlapping with or without the overlap soldered. The present invention is intended to overcome certain of the disadvantages associated with these prior constructions which disadvantages are enumerated below.

An inner conductor comprising a longitudinally folded tape with its longitudinal edges abutting is easily damaged when the cable is bent. Furthermore, a longitudinal folded tape with its edges abutting cannot grip the heart and when it is required to transmit any external grip on the cable to the heart, there is a danger that slip may occur between the inner conductor and the stranded heart. Also, since the abutting edges are not sealed, it is necessary to pass the inner conductor through a vacuum cham ber immediately before the insulation is extruded over it. Although the vacuum removes a large portion of the air contained in the interstices of the stranded heart, in certain cases, the heating effect of the extruded insulation causes the residual air in the interstices to expand, thus producing air bubbles in the extruded insulation. Not only does this complicate the extrusion process but it can also slow down the rate of extrusion of the insulation. The same disadvantage applies in lesser degree to the box-seamed tape, since the seam is not air tight.

If an inner conductor is used comprising a longitu dinally folded copper tape with overlapping edges soldered together, it is difiicult to obtain a tight grip upon the stranded heart in order that a grip upon the external surface of the cable may be transmitted to the stranded heart when it is composed of high tensile steel strands. Furthermore the soldered overlap may be damaged when the cable is bent.

According to the present invention, a method of manufacturing a submarine cable having insulation extruded over a conductor which surrounds a stranded metal heart, is characterized in that a longitudinally extending tape of metal, such as copper, of high electrical conductivity is folded or applied with its edges abutting around a torsionally balanced stranded metal heart, the abutting edges of the tape are butt welded together in a continuous seam 3 ,095,643 Eatented July 2, 1963 by means of inert gas shielded electric arc welding, and the tape so welded is reduced in diameter mechanically to connect the conductor and the heart together and thereby to inhibit relative movement between them. Inert gas shielded electric arc welding is wholly suitable for the welding process because the speed and control of Welding obtainable does not cause a stranded high tensile heart to be heated suiiiciently for it appreciably to lose any tensile strength.

By providing a continuous seam weld along the longitudinal edges of the folded metal tape, the air in the interstices of the stranded heart is prevented from escaping when expanded by the heating efiect of extrusion, and thereby air bubbles in the extruded insulation are avoided.

The conductor may be welded about the stranded heart as an over-size tube, and subsequently the tube containing the stranded heart drawn through a die or reducing rollers so that the tube is reduced in its cross-sectional dimensions to fit closely the stranded heart, the grip between the conductor and the stranded heart being thereby improved. Additionally, the oversize tube reduces risk of damage to the heart during welding.

In a preferred method in accordance with the invention of electrically Welding an inner conductor of copper tape about the stranded heart, which method will now be described by way of example with reference to the accompanying drawings in which FIGURE 1 shows a perspective cut back view of a cable and FIGURE 2 shows a cross section through a swaged steel heart, and FIG- URE v3 shows a view similar to FIGURE 1 embodying a modified form of the invention, the argon-arc method of electric welding is used and a single electrode torch having a vertically adjustable electrode fed by direct current is provided for welding purposes. One convenient construction of such a welding torch is described in the complete specification of British Patent No. 722,707.

Referring now to FIGURE 1 copper tape of between 0.007 to 0.030 inch thick preferably .015 inch thick, is fed horizontally from a reel to straightening rolls which also shear the longitudinal edges to provide clean edges for the argon-arc welding process. The copper tape is sheared to a width which will provide a folded tube 2 which is greater than that required for a close fitting tube around a stranded metal wire heart 1. The copper tape with its edges sheared is passed between forming rolls for folding it round the torsionally balanced stranded metal wire heart comprising four 0.092 inch diameter wires and twenty-six 0.038 inch diameter wires as disclosed in the Journal of the Institution of Electrical Engineers, volume 2 (new series) pages 572 to 573, October 1956, which may be fed vertically downwards from a supply drum and guided so as to feed horizontally into the folding copper tape. The copper tape when folded into the tube 2 completely encloses the stranded metal heart 1 which may be guided so as to press to the side of the copper tube 2 remote from the butting edges. The butting edges of the copper tape are then argon-arc welded together in a continuous seam as by a continuous weld 3 as shown between II and IIII, or alternatively as a stitch weld as shown at 4 between 11-11 and IIIIII, and the copper tube 2 thus welded is passed between one or more reducing dies or sets of rolls to compress it tightly upon the stranded metal heart 1. The outer diameter of the argon-arc welded inner conductor is then approximately 0.33 inch diameter and polythene insulation 5 is extruded over it with an outside diameter of approximately 1.00 inch. The outer conductor 6 is composed of six 0.50 inch wide by 0.018 inch thick aluminium tapes and is applied with a long lay to the extruded insu lation 5, a fabric tape 7 impregnated with a corrosion inhibitor, for example barium chromate, being applied over the aluminium tapes 6. A polythene outer sheath 8 of approximately 0.11 inch thick is extruded over the tape giving the cable an overall diameter of approximately 1.3 inches.

In some instances it may be desirable to provide protection for the stranded metal wire heart or any insulation which may surround it, against the heating due to weld ing the inner conductor. This may be done by including a copper foil 9 (see FIGURE 3) between the stranded metal wire heart and the copper tape before the latter is folded round it.

In an alternative construction of a submarine cable the outer conductor may be of copper instead of aluminium; additionally it may comprise a longitudinally folded copper or aluminium tape having either abutted or overlapped edges. If a copper outer conductor is used the corrosion inhibitor, with which the fabric '7 is impregnated, may be omitted.

If desired the outer sheath of polythene may be replaced by an outer sheath of a plastic material having a greater resistance to mechanical damage, such as polypropylene.

If it is found that the stranded metal wire heart is liable to bird-caging even when an over-size copper tube is electrically welded about it, this may be alleviated by passing the stranded metal wire heart through a die, which slightly reduces it in diameter by swaging, before it enters the fold in the copper tape. A cross section of a metal heart which has been swaged is shown in FIG- URE 2 where it can be seen that the strands are so deformed as to substantially fill the cross-sectional area of the heart. (To bird cage means to have an excessive tendency for the strands to bow radially outwards when the stranded heart is subjected to longitudinal compression.)

An electrically welded inner conductor for a submarine coaxial cable manufactured in accordance with the present invention has the following advantages over known constructions (1) An increased grip is provided between the inner conductor and'the stranded metal Wire heart. Thus, the inner conductor and heart are mechanically connected together to inhibit movement between them.

(2) The inner conductor is uniform in cross-section and it therefore is less likely to be damaged during bending. I

(3) Good electrical conductivity is provided across the electrical weld.

The method of locking the longitudinal edges of the copper tape together, which is at present in use, is by means of a box-seam and an electrically welded inner conductor has the following advantages over this method:

(1) The elimination of the protuberance results in:

(a) A reduction ofapproximately 3% in the capacitance and a corresponding increase in the inductance and therefore a reduction of approximately 3% in the attentuation of the cable.

(b) A greater breakdown voltage and therefore increased factor of safety because the stress concentration at the corners of the box-seam are no longer present.

(3) Complete sealing of the joined edges of the conductor.

(4) Better mechanical characteristics when the cable is bent.

A further advantage of the method according to the present invention is that because a torsionally balanced stranded metal heart is used, the inner conductor does not have to be of suflicient strength to limit or counteract any torsion produced by the heart and can, therefore, be relatively thin-thereby saving material.

We claim:

1. A method of manufacturing a submarine cable, said method comprising the steps of applying a longitudinally extending tape of copper of high electrical conductivity with its edges abutting around a torsionally balanced stranded metal heart, butt welding the abutting edges of the tape together in a continuous impermeable seam by means of inert-gas shielded electric arc welding so as to form an ensheathing tube, reducing the diameter of said tube so as to tightly compress said tube on the heart and thus mechanically connect the conductor and the heart together and thereby to inhibit relative movement between them, and thereafter heat extruding a plastic sheath over said tube and in contact therewith.

2. A method as set forth in claim -1 which is further characterized in that the tape is of a predetermined width so as loosely to surround the core and after welding is drawn down to eifect the mechanical connection between the heart and the conductor.

3. A method as set forth in claim 1 which includes the further step of drawing down the tape into intimate contact with the heart.

4. A method as set forth in claim 1 which includes the further step of providing a metal foil between the tape and the heart.

5. A method as set forth in claim 1 which includes the further step of initially completely swaging the stranded heart.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Post Office Electrical Engineering Journal (British publication), vol. April 1957, pages 7 and 8. 

1. A METHOD OF MANUFACTURING A SUBMARINE CABLE, SAID METHOD COMPRISING THE STEPS OF APPLYING A LONGITUDINALLY EXTENDING TAPE OF COPPER OF HIGH ELECTRICAL CONDUCTIVITY WITH ITS EDGES ABUTTING AROUND A TORSIONALLY BALANCED STRANDED METAL HEART, BUTT WELDING THE ABUTTING EDGES OF THE TAPE TOGETHER IN A CONTINUOUS IMPERMEABLE SEAM BY MEANS OF INERT-GAS SHIELDED ELECTRIC ARC WELDING SO AS TO FORM AN ENSHEATING TUBE, REDUCING THE DIAMETER OF SAID TUBE SO AS TO TIGHYLY COMPRESS SAID TUBE ON THE HEART AND THUS MECHANICALLY CONNECT THE CONDUCTOR AND THE HEART TOGETHER AND THEREBY TO INHIBIT RELATIVE MOVEMENT BETWEEN THEM, AND THEREAFTER HEAT EXTRUDING A PLASTIC SHEATH OVER SAID TUBE AND IN CONTACT THEREWITH. 